IT is a truth generally acknowledged that when Sarah Ferguson married Prince Andrew, second in line to the throne of Britain, she did not receive a copy of the House of Windsor playbook. As a result, this high-spirited commoner committed a number of youthful indiscretions that resulted in her being purged from the royal family. Saddled with what she considers an undeserved reputation as a spendthrift and freeloader, cast out into the darkness with two small children, Ms. Ferguson several years ago found herself foundering on the very shoals of fiscal disaster.

''As a single mother with few assets and less income than most presumed, I was in deep financial trouble,'' Ms. Ferguson recalls in her autobiography, ''My Story,'' harking back to those dark moments in 1992. Yet today, just five years later, the Duchess of York is well on her way to reversing her desperate financial situation. With the income from her Budgie the Little Helicopter children's books, the revenue stream generated by her just-published memoir and such potential gushers as a proposed endorsement deal with Weight Watchers International, Sarah Ferguson now appears to preside over a globe-spanning financial empire that stretches from the cobwebbed nooks of Covent Garden to the towering skyscrapers of Gotham.

By reinventing herself as a daring entrepreneuse, Sarah Ferguson has become, one might argue, a powerful role model for single mothers everywhere -- a heroic survivor. Yet, to date, the Duchess of York's re-emergence from the dank abyss of financial ruin has been obscured by the media's prurient obsession with her amorous peccadilloes. Now, with the publication of ''My Story'' and the virtually simultaneous appearance of books by her esteemed financial consigliere Allan Starkie (''I will never forget Nick Leeson and the friendship we forged'') and a savvy spiritual adviser named Madame Vasso (''You must be strong. You must not let them beat you''), it is possible to piece together the various strands of Ms. Ferguson's recent history and come to a fuller appreciation of the financial wizardry she has demonstrated.

The most pivotal moment in Ms. Ferguson's career occurred in November 1992, when she began researching a book about the travels of Queen Victoria. Although Ms. Ferguson had already earned a measure of literary fame with her 1989 children's book ''Budgie the Little Helicopter,'' and its remarkable sequel ''Budgie at Bendicks Point,'' these were not the types of publications likely to earn her critical respect. In 1991, she had participated in the publication of ''Victoria and Albert: Life at Osborne House,'' a picture book that ''was, in fact, too good for me to claim as my own creation.'' But another book about Queen Victoria might establish her as ''a serious person, a student of history.'' This would enable Ms. Ferguson to shed her reputation as a frivolous airhead, thus repositioning herself in an upmarket setting.

According to Allan Starkie, who landed his position as a financial adviser to Ms. Ferguson because of his business relationship with John Bryan, also her financial adviser, the Duchess made a critical decision during this period: she would actually travel with her co-author, Benita Stoney, and learn something about the life of Queen Victoria, just in case anyone asked. Not wishing to fall into the trap set for themselves by such authors as Charles Barkley and O. J. Simpson, both of whom claimed to have been misquoted in their ghostwritten autobiographies -- thus inviting jeers, catcalls and obloquy -- Ms. Ferguson elected to steep herself in the lore of Victoriana.

''The Duchess once bragged to me that she could field any question that was asked about her book on Victoria, even though she had never read it,'' Mr. Starkie recalls. Her cunning ploy paid off. As she proudly tells us, the book received good reviews and sold well, thus establishing Ms. Ferguson as a credible, sensible, marketable personality in her own right.

At this point, Ms. Ferguson sagaciously chose to play a game of cat and mouse with the consuming public. Indeed, the most interesting thing about her commercial ventures throughout the period 1993-95 is not what she did do, but what she did not do. According to Mr. Starkie, Ms. Ferguson briefly considered a number of money-making ventures but at the last minute gave the thumbs-down to all of them.

One suggestion put forth was that the Duchess produce a line of Windsor Castle plates that she could then market on QVC in the United States. A second was a series of novels set in London, based on a royal theme and featuring ''veiled autobiographical references.'' A third was a television mini-series tentatively titled ''Leave Them Smiling,'' in which ''the Duchess would travel into Eastern Europe and find some hellish place in some way associated with children. Via the cameras, she would draw public attention to its plight, raise money for its sick or starving or dispossessed and then go back and graciously hand the check over.''

Although any one of these ventures would have generated copious revenue for the Duchess and her impoverished children, each proposal was ultimately voted down. According to Mr. Starkie, the royal plate idea ''had come to nothing because Wedgwood wanted the fabrication costs of the plate up front -- the manufacturer's minimum run of 10,000 plates would have cost

150,000, which the Duchess did not have.'' The series of novels was ditched, presumably because of an insufficient advance proposed by the publisher. And although Mr. Starkie does not say so himself, one gets the clear impression that the mission of mercy to Eastern Europe was scrapped because it was tainted by just the faintest hint of cheesiness. (So too the proposal for a chain of Duchess of York Nursing Homes, for which she would receive ''
1 per bed per night for each person in the homes.'')

Undaunted by these setbacks, Mr. Starkie suggested that Ms. Ferguson paint a watercolor depicting Windsor Castle, which would then be turned into ''a limited-edition lithograph,'' again to be sold on QVC. Ms. Ferguson said no. Yet another alternative was to borrow a painting of the castle done by Queen Victoria from the Royal Archives. This idea was apparently given serious consideration, but was eventually nixed because it was deemed ''most unlikely'' that Queen Elizabeth would ever give her approval to such a plan.

Still a single mother, still crushed beneath a mountain of debt, the Duchess of York could easily have succumbed to the temptation to cash in on such downscale ventures as presiding over a series of luncheons at which complete strangers would pay

100,000 to dine with her. To her credit, Ms. Ferguson rejected these penny-wise, pound-foolish schemes, fearing that tawdry, supplicant business enterprises like these would destroy her image forever. Instead, she quietly, diligently continued her campaign of personal reconstruction.

The most critical moment in this rehabilitation process occurred in March 1996, when Ms. Ferguson competed in the International Qatar Horse Marathon, sometimes known as ''Desert Storm.'' This grueling 26-mile race served as an international platform on which a slimmer, fitter, more mature Sarah Ferguson could reintroduce herself to an astonished public. What's more, by riding in a team that finished third in a competition in which the beloved movie star Patrick Swayze had finished dead last just one year earlier, Ms. Ferguson demonstrated that she was not just some calculating jet setter scavenging for a few lines of free press but a gifted horse personage in her own right. Yes, it was Ms. Ferguson's electrifying performance in the International Qatar Horse Marathon that sent a clear and positive message to the public: The Duchess of York is back in the saddle.

In the months since her equestrian triumph in Qatar, Sarah Ferguson has taken America by storm. Hugely successful appearances on ''Good Morning America'' and ''The Rosie O'Donnell Show,'' coupled with fawning media coverage in outlets as varied as People and The Wall Street Journal, have propelled Ms. Ferguson into the public-relations stratosphere. Though the Duchess is certain to profit enormously from the publication of ''My Story'' and her two new children's books, ''The Royal Switch'' and ''Bright Lights,'' it is the putative arrangement with Weight Watchers International that could insure her financial heft for many years to come. To the illustrious pantheon of female financial titans that range from Coco Chanel to Katharine Graham to Madonna Ciccone can now be added one more name: The Fergmeister.

Readers interested in learning more details about Sarah Ferguson's spectacular rebirth as a self-iconizing entrepreneuse are advised to skim Madame Vasso's slim volume but to study diligently Mr. Starkie's copiously detailed tome. However, to understand fully Ms. Ferguson's acumen, it is necessary to read ''My Story'' from cover to cover. Like Sam Walton and Donald Trump before her, Ms. Ferguson has written a seminal primer on the psyche of the entrepreneur, bristling with homespun wisdom sure to be passed down from generation to generation. Here are just a few examples:

* ''When you lie down with dogs, you can't be shocked to get fleas.''

* ''When you lie down with a wolf, you must count yourself lucky to come out with your jugular intact.''

* ''I have always sailed close to the wind, through storm and calm, and over the roughest whitecaps.''

But, most important, anyone wishing to emulate Ms. Ferguson should bear these words in mind:

* ''When you have touched the flames of hell, a branding iron is only a mild inconvenience.''